Over the last decade, it’s become a rite of passage for NorCal big-wave riders: Go to Ocean Beach on the swell of the season. Wax up your biggest gun when, seemingly, no one else has the sack for it. After an hour of brutal beatings you emerge, victorious, on the outer bars, where house-sized A-frames detonate forlornly. And that’s when you spot her: a middle-aged woman with an orange swim cap, bodysurfing down the face of a bomb. Depending upon the ego involved, Judith Sheridan is likely to incite chagrin, confusion, or awed admiration among hellmen. Perhaps mountaineers feel the same way when they rely on equipment to accomplish what their Sherpa does with relative ease. But Judith is no Sherpa—instead, she is a 49-year-old geophysicist from Detroit, whose first real experience riding waves came a little more than a decade ago. She’s improbably transitioned from lake swimming, to ocean swimming, to bodysurfing, to bodysurfing Maverick’s.

Technically speaking, this makes her a true maverick—she has never considered herself one of the “tribe,” and it’s only recently that surfers have begun to appreciate the depth of Judith’s courage and abilities. The whole reason she began bodysurfing big waves was to get away from surfers. She suffered routine drop-ins in crowded conditions, as surfers serially underestimate Sheridan’s ability to make waves. After a broken nose and broken clavicle, she retreated to the outer bars to find some peace.

“When I’m in the water, I feel most like myself,” Judith explains. She feels steadier, more aware, more in control. It’s only in recent years that Judith found a medical explanation for this feeling. In 2008, after years of problems with balance and a degradation of sight in her right eye, Sheridan was diagnosed with multiple sclerosis. Her physicians estimate she’s been fighting the disease for 25 years. Judith notes that heat activates MS lesions in her brain, meaning cold Northern California water provides therapeutic benefits. Judith is hesitant to let MS define her, but she admits, “MS has directed my takeoff style and how I ride a wave.” She has developed a unique underwater takeoff to compensate for the loss of strength in her arms. She’s utilized this style at Maverick’s over the course of a few dozen sessions. Despite her condition, she feels lucky. “MS has freed me—it’s license to do what I want.”

In a male-dominated sport, where women are displayed as blonde teenagers in bikinis (if at all) it’s hard to process Sheridan. She literally finds herself alone, in the dark, murky water that most casual surfers strive to avoid: swimming, without a surfboard, in the bowl at Mavericks’s, with vision and muscle-tone degraded by a debilitating neurological disease. While self-proclaimed legends win $50,000 for letting go of a tow rope, Judith inhabits our cold nightmares and makes them her solace and retreat. Sheridan notes, “I like to keep my head down and pretend I’m invisible.” She’s not.